Amplifying circuit for an integrated circuit with low-noise characteristic

ABSTRACT

An amplifying circuit is suitable for an integrated circuit that has a characteristic of low-noise, high-gain, and low-consumptive current. In the circuit, transistors or FETs are used as amplifying elements. A basic amplifying circuit employing transistors, that forms a differential pair of first and second transistors, first and second resistors connected to each collector of the first and second transistors, and a constant current source connected to a common emitter of the first and second transistors, comprises a third transistor, of which emitter is connected to a connecting point of the first and second resistors, a condenser connected between a connecting point of the first transistor and the first resistor, or a connecting point of the second transistor and the second resistor, and a base of the third transistor, and a voltage source connected to a collector of the third transistor, wherein outputs are obtained from an emitter of the third transistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an amplifying circuit. More particularly, it relates to an amplifying circuit, which is suitable for an integrated circuit with the low-noise, high gain and low power consumption characteristics.

2. Description of the Prior Art

In recent years, movable communication terminals, such as a portable telephone, are spreading extensively. According to this fact, there is a demand for making a circuit of high frequency characteristic used for movable communication terminals, such as a portable telephone, micro-miniaturized. Moreover, there is also a demand for making an amplifying circuit, which has been composed of individual parts integrated.

Further, most of the movable communication terminals, such as a portable telephone, are driven with batteries. Accordingly, it is required to reduce current consumption for lengthening the period of life of a battery.

FIG. 19 is one structural example of a conventional transistor amplifying circuit.

In the diagram, a constant-current source I₀ and a condenser C_(E) connected to the constant-current source in parallel are connected to the emitter of a first transistor Q₁. Also, a voltage source V_(CC) is connected to the collector of the transistor Q₁, via a load-resistor R_(C). A bias voltage V_(BB) is supplied to the base of the transistor Q₁.

Further, the conventional transistor amplifying circuit includes a second transistor Q₂, of which the collector is connected to the voltage V_(CC) and the emitter is connected to a resistor R_(E). Furthermore, an output from the collector of the first transistor Q₁ is connected to the base of the second transistor Q₂.

Moreover, the base of the transistor Q₁ is used as an input terminal of a high-frequency signal, and the emitter of the transistor Q₂ is used as an output terminal of the high-frequency signal. In this circuit, the transistor Q₁ is an amplifying circuit of an emitter grounded type, and the transistor Q₂ forms an emitter follower circuit for matching impedance with the circuit arranged behind the emitter follower circuit.

FIG. 20 further illustrates a structural example of the conventional transistor amplifying circuit including a bias circuit section 21. As is apparent from FIG. 20, the transistor amplifying circuit is composed of the amplifying circuit section 20 and the bias circuit section 21 for supplying a bias voltage required to each portion of the amplifying circuit.

In FIG. 20, the amplifying circuit section 20 corresponds to the transistor amplifying circuit shown in FIG. 19. The amplifying circuit section has a transistor Q₃ and a resistor R_(E1), instead of the current source I₀ shown in FIG. 19 and a transistor Q₁ and a resistor R_(E2), instead of the resistor R_(E) shown in FIG. 19.

The bias circuit section 21 shown in FIG. 20 supplies bias current source, that is, base potential of the transistors Q₁, Q₂, Q₃, and Q₄, required for the amplifying circuit section 20 positioned on the right side of the circuit of FIG. 20. The bias circuit section 21 is composed of a 2-line structured constant current circuit which has three transistors Q_(B1) to Q_(B3), and three transistors Q_(B4) to Q_(B6) laid lengthwise, respectively. Further, the transistors Q_(B2) to Q_(B3) and Q_(B5) to Q_(B6) function as diodes by connecting the bases and the collectors in common.

Meanwhile, in the transistor amplifying circuit of an emitter grounded type shown in FIGS. 19 and 20, noise amount (NF) of the circuit is generally proportional to the resistance of base resistor R_(b) of a transistor used. Further, it is generally known that noise amount (NF) is inversely proportional to the second power of f_(t) (cutoff frequency) of a transistor.

In FIGS. 19 and 20, a resistor R_(C) is a collector load resistor of transistor Q₁, which is an amplifying element. At the same time, the resistor R_(C) also has a function of dropping the voltage to a suitable base potential of the transistor Q₂ of the emitter follower circuit, which follows the transistor Q₁.

In the above-described transistor amplifying circuit shown in FIGS. 19 and 20, collectors of the transistors Q₁ and Q₂ are connected to the voltage source V_(CC), respectively. Therefore, a consumption current of the amplifying circuit becomes the sum (I₁ +I₂) of the current I₁, flowing into the transistor Q₁ and the current I₂ flowing into the transistor Q₂.

Thus, when making the consumption current lower in this circuit, it becomes necessary to reduce both, the current I₁ and the current I₂. Accordingly, it brings a problem that the performance of the circuit is not sufficiently fulfilled in the case where the circuit is used as an amplifying circuit. Or, it brings another problem that the consumption current becomes large in the case where a satisfactory performance is obtained.

It also becomes necessary to have two rows of the circuits forming the bias circuit section 21, in FIG. 20. Therefore, the consumption current in the bias circuit section 21 becomes the sum (I_(B1) +I_(B2)) of the currents I_(B1) and I_(B2), which respectively flow to each of constant current circuits, as well as in the amplifying circuit section 20. Accordingly, the circuit can not make the current amount lower.

Further, the base resistor R_(b) of the grounded-emitter type transistor Q₁ is practically determined according to the physical forms of individual transistors in general. Furthermore, the cutoff frequency f_(t) is also determined according to the semiconductor process technique for manufacturing transistors.

If the current of the transistor amplifying circuit is made lower, there is a tendency that the cutoff frequency f_(t), becomes lower and the noise amount becomes worse.

The V_(ce) (voltage between the collector and the emitter) of the transistor Q₁ becomes smaller because of the voltage drop with the load resistor R_(c). It is generally known that the cutoff frequency f_(t) of a transistor becomes lower, if the V_(ce) of the transistor as large as possible, more particularly, in the case where a high-frequency circuit is required.

In another mode, an amplifying circuit is composed of a differential pair of transistors. FIG. 21 is a diagram showing one example of a conventional differential amplifying circuit composed by the differential pair of transistors.

In the diagram, the emitters of a pair of transistors Q₁₁ and Q₁₂ are connected in common, and connected to the constant current source I₀. Further, the collectors of both transistors Q₁₁ and Q₁₂ are connected to the load resistors R_(C1) and R_(C2), respectively. Furthermore, the load resistors R_(C1) and R_(C2) are connected to the voltage source V_(CC).

In the differential amplifying circuit having the above-described structure, the current I_(C1) flows to the collector of the transistor Q₁₁ and the current I_(C2) flows to the collector of the transistor Q₁₂ according to the structure. If the current I_(C1) is equal to the current I_(C2), twice amount of current flows in comparison with that of the circuit having a single-end structure formed of the transistor Q₁ shown in FIG. 19.

If the current is reduced, the output driving ability becomes lower. When the low impedance load is further connected, the characteristic of the circuit is deteriorated. Accordingly, as shown in FIG. 22, another transistor Q₁₃ is connected to be an emitter follower, similarly to the conventional circuit shown in FIG. 19. There have been frequent cases where the load of the differential amplifying circuit is reduced in this fashion.

However, the consumption current becomes larger, in either case, if a larger current flows to the differential amplifying circuit, and if the emitter follower circuit is connected to reduce the current of the differential amplifying circuit.

Further, in the above description of the prior art, the amplifying circuit is formed by transistors. Alternatively, FIG. 23 shows a prior art of the differential amplifying circuit formed by FETs (Field Effect Transistors).

The differential pair is formed by two FETs T₁₁ and T₁₂, the source terminals of which are mutually connected. Further, the commonly connected source terminals are grounded via the constant current source I₀. The consent current source I₀ controls the sum (I₁₁ +I₁₂) of the currents flowing from the drain voltage V_(d1) to two FETs T₁₁ and T₁₂ so as to become constant.

The gate terminals of the FETs T₁₁ and T₁₂ are a non-inverse input terminal I and an inverse input terminal /I (hereinafter used /I means inversion of I), respectively, and the terminals are similarly connected to the gate bias voltage V_(g).

The drain terminals of the FETs T₁₁ and T₁₂ are connected to the drain voltage V_(d1) via the resistors R₁₁ and R₁₂, respectively. The drain terminals are connected to the gate terminals of the FETs T₁₃ and T₁₄, respectively.

The drain terminals of FETs T₁₃ and T₁₄ are connected to the drain voltage V_(d2), respectively. Further, the source terminals of the FETs T₁₃ and T₁₄ are grounded via the resistors R₁₃ and R₁₄, respectively, and simultaneously become a non-inverse output O and an inverse output /O (hereinafter used /0 means inversion of 0), respectively.

In this way, the differential amplifying circuit is symmetrical. The used FETs are also arranged symmetrically, and the current I₁₁ flowing to the FET T₁₁ is equal to the current I₁₂ flowing to the FET T₁₂. Simultaneously, the current I₁₃ flowing to the FET T₁₃ becomes equal to the current I₁₄ flowing to the FET T₁₄.

In the conventional circuit, the part composed of FETs T₁₁ and T₁₂, constant current source I₀ and resistors R₁₁ and R₁₂ is a basic differential amplifying circuit. The FETs T₁₃ and T₁₄ form source follower circuits for matching the output impedance.

Here, the reason for providing the source follower circuit is the same as explained in connection with the conventional circuit shown in FIGS. 19 and 22. More particularly, it is known to use the characteristic impedance of 50 ohms when connecting high frequency circuits. However, the differential amplifying circuit has a high output impedance, so that an amplified signal cannot be outputted effectively, if the output terminal of the amplifying circuit is connected to a circuit having the characteristic impedance of 50 ohms, as it is. Therefore, the source follower circuit is required for conversing the impedance.

In such FET differential amplifying circuit, the difference of two high-frequency signals inputted to the non-inverse input terminal I and the inverse input terminal /I is amplified to output to the non-inverse output terminal O and the inverse output terminal /O, respectively.

The signals outputted from the non-inverse output terminal 0 and the inverse output terminal /0 have phases reversed with same amplitude.

FIG. 24 is a diagram showing the structure of an amplifying circuit formed by using the differential amplifying circuit shown in FIG. 23. As compared with the circuit shown in FIG. 23, the constant current source I₀ is replaced with resistor R₁₇, and it is grounded via resistors R₁₅ and R₁₆ instead of the gate bias voltage V_(g). Accordingly, the circuit realizes a self-biasing system.

According to the FET differential amplifying circuit having the structure shown in FIG. 24, it becomes possible to amplify and output high-frequency signals supplied to the non-inverse input terminal I and the inverse input terminal /I from the non-inverse output terminal O and the inverse output terminal /0, stably.

However, FETs T₁₂ and T₁₄ are connected to the drain voltages V_(d1) and V_(d2), respectively, as well as FETs T₁₁ and T₁₃ in the FET differential amplifying circuit shown in FIGS. 23 and 24. Therefore, the consumption current becomes a ground total of the sum (I₁₁ +I₁₃) of the currents flowing to the FETs T₁₁ and T₁₃ and the sum (I₁₂ +I₁₄) of the currents flowing to the FETs T₁₂ and T₁₄.

Accordingly, the consumption current of the circuit becomes larger. In such amplifying circuit having the above-described structure, it is required to reduce both the sum of I₁₁ +I₁₃ and the sum of I₁₂ +I₁₄, in order to make the consumption current lower. Consequently, it brings a problem that the circuit does not sufficiently fulfill its function as a differential amplifier because the gain is reduced.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an amplifying circuit, which is suitable for an integrated circuit with characteristics of high gain, low-noise and low-current consumption, without losing its amplifying function and which can overcome the problems which are commonly known to the conventional amplifiers as described above in detail.

It is another object of the present invention to provide an amplifying circuit composed of transistors, which can have a low current consumption.

It is still another object of the present invention to provide a differential amplifying circuit having a differential pair of transistors, which is suitable for an integrated circuit with a low current consumption.

It is a further object of the present invention to provide a FET differential amplifying circuit suitable for an integrated circuit (MMIC) that is low-noise and can make the consumption current lower.

The transistor amplifying circuit according to the present invention has a basic structure as follows:

The circuit comprises a first transistor (Q₂) having a base coupled to an input terminal, and to which a first base bias (V_(B1)) is supplied; a second transistor (Q₂) having a collector connected to a voltage source (V_(CC)), a base supplied with a second base bias (V_(B2)) and an emitter coupled to an output terminal (OUT); a parallel circuit of a constant current source (I₀) connected to an emitter of the first transistor (Q₁) and a first condenser (C_(E)); an inductor (I_(C)) connected between a collector of the first transistor (Q₁) and an emitter of the second transistor (Q₂); and a second condenser (C_(c)) connected between the collector of the first transistor (Q₁) and the base of the second transistor (Q₂).

Further, the transistor differential amplifying circuit according to the present invention has a basic structure as follows:

The circuit comprises a differential pair including first and second transistors, first and second resistors connected to collectors of the first and second transistors and a constant current source connected commonly to emitters of the first and second transistors, a third transistor, an emitter of which is connected to a connection point of first and second inductors; a first condenser connected between the collector of the first transistor and a base of the third transistor; and a voltage source connected to the collector of the third transistor, an output being outputted from the emitter of the third transistor.

Furthermore, the FET differential amplifying circuit according to the present invention has a basic structure as follows:

The circuit comprises a differential pair including first and second FETs; first and second resistors respectively connected to the drains of the first and second FETs and a constant current source connected between a commonly connected source of the first and second FETs and ground; third and fourth FETs, the drains of which are respectively connected to the first and second resistors, a voltage source connected to the sources of the first and fourth FETs; and a gate bias source for supplying gate biases to the gates of the first and second FETs; the drain of the first FET being connected to the gate of the third FET, the drain of the second FET being connected to the gate of the fourth FET and the gates of the first and second FETs being supplied with a non-inverted input and an inverted input, respectively.

Other objects and advantages of the present invention will become apparent from the detailed description to follow taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and detailed description of the preferred embodiments to follow, explain the principle of the invention.

FIG. 1 is a schematic diagram showing a first embodiment of a transistor amplifying circuit according to the present invention;

FIG. 2 is a schematic diagram showing a second embodiment of a transistor amplifying circuit according to the present invention;

FIG. 3 is a schematic diagram showing a third embodiment of a transistor amplifying circuit having a bias circuit section according to the present invention;

FIG. 4 is a schematic diagram showing a fourth embodiment of a transistor amplifying circuit having a bias circuit section according to the present invention;

FIG. 5 is a schematic diagram showing a fifth embodiment of a transistor amplifying circuit having a bias circuit section according to the present invention;

FIG. 6 is a schematic diagram showing a first embodiment of a transistor differential amplifying circuit according to the present invention;

FIG. 7 is a schematic diagram showing a second embodiment of a transistor differential amplifying circuit according to the present invention;

FIG. 8 is a schematic diagram showing a third embodiment of a transistor differential amplifying circuit according to the present invention;

FIG. 9 is a schematic diagram showing a fourth embodiment of a transistor differential amplifying circuit according to the present invention;

FIG. 10 is a diagram for explaining a control operation of the embodiment shown in FIG. 9;

FIG. 11 is a schematic diagram showing a fifth embodiment of a transistor differential amplifying circuit according to the present invention;

FIG. 12 is a schematic diagram showing a first embodiment of a FET differential amplifying circuit according to the present invention;

FIG. 13 is a schematic diagram showing a more specific first structural example of the embodiment shown in FIG. 12;

FIG. 14 is a schematic diagram showing a more specific second structural example of the embodiment shown in FIG. 12;

FIG. 15 is a schematic diagram showing a second embodiment of a FET differential amplifying circuit according to the present invention;

FIG. 16 is a schematic diagram showing a third embodiment of a FET differential amplifying circuit according to the present invention;

FIG. 17 is a schematic circuit showing a fourth embodiment of a FET differential amplifying circuit according to the present invention;

FIG. 18 is a schematic circuit showing a fifth embodiment of a FET differential amplifying circuit according to the present invention;

FIG. 19 is a first example of a conventional transistor amplifying circuit;

FIG. 20 is a second example of a conventional transistor amplifying circuit having a bias circuit section;

FIG. 21 is a first example of a conventional transistor differential amplifying circuit;

FIG. 22 is a second example of a conventional transistor differential amplifying circuit;

FIG. 23 shows a prior art of a FET differential amplifying circuit; and

FIG. 24 shows a specific structural example of the conventional circuit shown in FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic diagram showing a first embodiment of a transistor amplifying circuit according to the present invention.

In FIG. 1, the circuit has a first transistor Q₁ and a second transistor Q₂. The transistors Q₁ and Q₂ are laid lengthwise and are directly connected for a direct current.

A constant current source I₀ is connected to an emitter of the first transistor Q₁, and a condenser C_(E) is connected to the emitter of the first transistor Q₁ in parallel with condenser C_(E). A collector of transistor Q₁ is connected to an emitter of the transistor Q₂ via a load inductor L_(C).

Further, the collector of the first transistor Q₁ is connected to a base of the second transistor Q₂ via a condenser C_(C). The condenser C_(C) has a function of separating the collector of transistor Q₁ from the base of transistor Q₂ for a direct current, and connecting them for an alternating current.

The collector of the transistor Q₂ is connected to a voltage source V_(CC), and the base of the transistor Q₂ is connected to a bias voltage V_(B2). The base of the transistor Q₁ is connected to a bias voltage V_(B1).

Furthermore, a signal of high-frequency is inputted to the input terminal IN, that is, the base of the transistor Q₁. The high-frequency output amplified is supplied from the collector of the transistor Q₁ via the condenser C_(C) to the base of the transistor Q₂, and is outputted from the emitter of the transistor Q₂.

In this circuit, the transistor Q₁ forms a grounded-emitter type amplifying circuit, and the transistor Q₂ forms a grounded-collector type emitter follower amplifying circuit. The inductor L_(C) becomes a collector load of the transistor Q₁.

More particularly, in the circuit according to the present embodiment, the inductor L_(C) has a high impedance for the frequency that is used. Therefore, the signal amplified by the transistor Q₁ can be supplied to the base of the transistor Q₂ effectively. Accordingly, loss at high frequency can be prevented.

Further, there is no drop of the direct voltage in the inductor L_(C), so that voltage V_(ce) between the collector and the emitter of the transistor Q₁ can be sufficiently maintained. Therefore, the transistor can be operated without losing the original performance of the transistor.

Furthermore, only one circuit is connected to the voltage source V_(CC) as a result by laying the transistors Q₁ and Q₂ lengthwise in a line, as described above. It becomes possible to make a current I₃ flowing to the whole circuit less than the sum of the consumption currents I₁ and I₂ of the conventional circuit shown in FIGS. 19 and 21.

FIG. 2 shows a second embodiment of the transistor amplifying circuit according to the present invention. As compared with the embodiment shown in FIG. 1, a bias voltage is applied to the base of the transistor Q₂ by connecting the base to the voltage source V_(CC) via a resistor R_(C). Further, the constant current source I₀ is formed by the resistor R_(E).

This circuit is used in the case where it can be operated even if the base potential of the transistor Q₂ is higher to some extent. Two voltage sources V_(CC) and V_(BB) can supply the bias required for the whole circuit. Therefore, no bias circuit for biasing the base of the transistor Q₂ is necessary, the circuit can be miniaturized, and, the current of the circuit can be made lower.

FIG. 3 shows a third embodiment of the transistor amplifying circuit according to the present invention. This circuit has a bias circuit section 31 for supplying required bias voltages on the basis of the transistor amplifying circuit shown in FIG. 1.

In the transistor amplifying circuit section 30, the constant current source I₀ is composed of a third transistor Q₃ and resistor R_(E), on the basis of the amplifying circuit shown in FIG. 1.

Consequently, the circuit requires the bias source for supplying the bias voltage to the base of the transistors Q₁, Q₂ and Q₃. The bias circuit section 31 becomes the bias source.

In this bias circuit section 31, each base of the transistors Q_(B1), Q_(B3), and Q_(B4) is connected to each collector of the transistors. Therefore, the transistors function as diodes for shifting voltage.

Further, the transistor Q_(B2) is provided between transistors Q_(B1) and Q_(B3). The base of the transistor Q_(B2) is supplied with a constant voltage V_(BB) from a bias supplying circuit, not shown in the diagram.

In the bias circuit section 31, the constant voltage of voltage source V_(BB) is supplied to the base of the transistor Q_(B2). The transistors Q_(B1), Q_(B3), and Q_(B4) generate voltages required, as voltage level shift circuits, respectively. Accordingly, the required bias voltages are supplied via base bias resistors R_(B2) to R_(B4), to the corresponding bases of the amplifying circuit section 30, which is composed of the transistors Q₁, Q₂ and Q₃ connected lengthwise.

In this way, only one line is connected to the voltage source V_(CC) at last, in the bias circuit section 31, because the bias circuit section 31 has its elements connected lengthwise in a line, similarly to the amplifying circuit section 30. Therefore, it becomes possible that the current I_(B3) flowing to the circuit is less than the sum of the consumption currents I_(B1) and I_(B2) shown in the conventional bias circuit section 21 of FIG. 20.

FIG. 4 shows a fourth embodiment of the transistor amplifying circuit according to the present invention. This circuit has a bias supplying circuit 32 for supplying required bias voltage on the basis of the amplifying circuit including the bias circuit section 31 shown in FIG. 2.

The amplifying circuit section 30 is the same as the circuit shown in the embodiment of FIG. 2. Accordingly, the required bias voltage is only a base bias supplied to the base of the first transistor Q₁. The base bias voltage V_(rem) is supplied via the base bias resistor R_(B) from the bias supplying circuit 32 to the base of the transistor Q₁.

In the embodiment shown in FIG. 4, only one base bias voltage may be supplied, so that there is no need to use the bias circuit section 31 that forms a level shift circuit as explained in connection with the embodiment shown in FIG. 3. This circuit includes only a bias supplying circuit 32 that functions as a constant voltage supplying circuit.

FIG. 5 shows a fifth embodiment of the transistor amplifying circuit according to the present invention. The circuit has the bias circuit section 31. The bias circuit section 31 has the same structure as the circuit 31 shown in the embodiment of FIG. 3.

The difference between this embodiment and the embodiment shown in FIG. 3 is that, in order to improve efficiency, a resonant tank circuit is formed with a condenser C'_(c) and an inductor L'_(C), instead of the inductor L_(C) that is inserted to the emitter of the second transistor Q₂ in the amplifying circuit section 30. The remaining structure of this circuit is the same as that of the embodiment shown in FIG. 3.

It will be apparent from the above-described embodiments that the transistor amplifying circuit according to the present invention is suitable for an integrated circuit. More particularly, in the case where the transistor amplifying circuit according to the present invention is incorporated in an integrated circuit, the following advantages can be obtained by making the size of emitter E_(Q1) of the transistor Q₁ larger than the size of emitter E_(Q2) of the transistor Q₂.

That is, emitter current density becomes smaller and the base resistor R_(b) that is determined according to a physical form is reduced, if the size of the emitter of the transistor is made larger. Therefore, the noise amount NF of the circuit is improved.

Further, the size of the emitter E_(Q2) is made smaller than the size E_(Q1) to make the circuit high impedance for the voltage V_(CC) and prevent the circuit from loss of high frequency. Therefore, it is possible to keep the NF of the amplifying circuit suitable, even if the current is made lower in the circuit, although it is known that it is lowered, and the noise amount NF is deteriorated when the current of a transistor is decreased.

FIG. 6 shows a first embodiment of a transistor differential amplifying circuit according to the present invention. As compared with the conventional transistor differential amplifying circuit shown in FIG. 22, the constant current source I₀ is connected in common to an emitter of each of the transistors Q₁₁ and Q₁₂.

Further, a resistor R_(C1) connected to a collector of the transistor Q₁₁ is connected to a resistor R_(C2) connected to a collector of the transistor Q₁₂ in common. A transistor Q₁₃ forming a buffer circuit is connected between commonly connected resistors R_(C1) and R_(C2) and the voltage source V_(CC) in series for a direct current.

Furthermore, a condenser C is connected between the base of the transistor Q₁₃ and one of the transistors Q₁₁ and Q₁₂ that constitute a differential pair, i.e., the collector of the transistor Q₁₁. The condenser C cuts off between the base of the transistor Q₁₃ and the collector of the transistor Q₁₁, for a direct current, or connects them for an alternative current.

Complementary signals, of which amplitudes are the same and phases of which are reversed, are inputted to the bases of the transistors Q₁₁ and Q₁₂.

In the circuit explained above, the current I_(C) flowing to the transistor Q₁₃ that forms the buffer circuit diverts into the transistors Q₁₁ and Q₁₂ that form a differential pair, as it is. Therefore, all current becomes I_(C) =I_(C1) +I_(C2). As compared with I_(C) =I_(C1) +I_(C2) +I_(C3) in the case of the conventional circuit shown in FIG. 22, the circuit can make the consumption current lower.

Further, it becomes possible that the emitter resistor R_(E) required in the conventional circuit shown in FIG. 22 be omitted, so that the structure of the circuit can be made simple.

In the case where transistors of the same emitter size are used as the transistors Q₁₁, Q₁₂, and Q₁₃, the current density of the transistor Q₁₁ and Q₁₂ becomes smaller in comparison with that of the transistor Q₁₃. Simultaneously, it becomes possible to make the noise amount better.

Furthermore, it becomes possible to obtain an amplifying circuit having a large gain, of which noise amount is better by making the emitter size of the transistors Q₁₁ and Q₁₂ larger than that of the transistor Q₁₃.

The transistor Q₁₃ does not significantly affect the noise amount. Because of that, it is possible to prevent circuit losses by making the emitter size of the transistor Q₁₃ smaller so as to obtain a high impedance for the voltage V_(CC).

FIG. 7 shows a second embodiment of the transistor differential amplifying circuit according to the present invention. More particularly, it shows a structural example of the transistor differential amplifying circuit provided with a bias circuit section.

A differential amplifying circuit composed of the transistors Q₁₁, Q₁₂, and Q₁₃ has the same structure as the circuit shown in the embodiment of FIG. 8.

The bias supplying section is composed by the series connected transistors Q_(B1) to Q_(B3) provided between the voltage V_(CC) and the ground and the resistor R_(BE). The transistors Q_(B1) to Q_(B3) are elements that generate the base bias voltages, respectively, for the corresponding transistors Q_(B1) and Q_(B3) are connected to the bases thereof, respectively, to function as diodes for level shifting.

Therefore, the base bias voltages are generated from the bias voltage of one constant voltage source V_(BB). Simultaneously, the bias voltages are applied via the base resistors R_(B1), R_(B2), and R_(B3) to the bases of the corresponding transistors Q₁₁, Q₁₂, and Q₁₃, respectively.

The bias supplying section in this circuit is also connected to one voltage V_(CC) as well, as explained in connection with FIGS. 3 and 5. Accordingly, it becomes possible to make the structure of the circuit simple and reduce the consumption current.

FIG. 8 shows a third embodiment of the transistor differential amplifying circuit according to the present invention. As compared with the embodiment shown in FIG. 7, resistor R_(B3) is provided between the base of the transistor Q₁₃ and the voltage source V_(CC), without obtaining the base bias of the transistor Q₁₃ from the bias supplying section. Therefore, the circuit can be made simple.

That is, the circuit from the transistor Q_(B1) to the resistor R_(B3) in the bias supplying section shown in FIG. 7 is omitted, and it also becomes possible that the current flowing in the amplifying circuit be lowered.

FIG. 9 shows a fourth embodiment of the transistor differential amplifying circuit according to the present invention. As compared with the embodiment shown in FIG. 8, a condenser C_(B) is provided between the base of the transistor Q₁₂ and the ground to short cut the input terminal for high frequency and further, the direct bias is controlled by the control signal V_(CONT) supplied to the resistor R_(CONT).

Accordingly, the gain is changed by the variation of the direct bias, so that the circuit forms a variable gain amplifying circuit, the gain of which is converted by the control signal V_(CONT). As shown in FIG. 10, the gain is changed from G₁ to G₂, by changing the control signal V_(CONT) from V₁ to V₂.

FIG. 11 shows a fifth embodiment of the transistor differential amplifying circuit according to the present invention. As compared with the embodiment shown in FIG. 8, the collector resistors R_(C1) and R_(C2) of a pair of transistors Q₁₁ and Q₁₂ in the differential amplifying circuit are replaced with inductors L_(C1) and L_(C2).

Therefore, the direct-current voltage impressed to each transistor becomes larger, so that the high-frequency differential amplifying circuit that can obtain a high output can be formed.

Although the embodiment of the amplifying circuit using the transistors as amplifying elements and a differential amplifying circuit has been explained, modifications may be made according to this invention by using the basic principles in such circuits. For example, a FET can be used as an amplifying element.

FIG. 12 shows a first embodiment of a differential amplifying circuit using FETs, according to the present invention.

The FET differential amplifying circuit is composed of a differential pair of two FETs T₁ and T₂, and FETs T₃ and T₄ for a source follower provided at each drain terminal of the differential pair, which are laid lengthwise in a line, for one voltage V_(d1).

That is, as shown in FIG. 12, the differential pair is formed by commonly connecting the source terminals of two FETs T₁ and T₂, and the common source terminal connected to the constant current source I₀ is grounded.

The gate terminals of the FETs T₁ and T₂ make the non-inverse input terminal I and inverse input terminal /I, respectively, and together, the gate terminals are connected to the gate bias voltage V_(g). The drain terminals of the FETs T₁ and T₂ are connected to the source terminals of the FETs T₃ and T₄ via the resistors R₁ and R₂.

The drain terminals of the FETs T₃ and T₄ are connected to the voltage V_(d1), respectively. Further, the source terminals of the FETs T₃ and T₄ become the non-inverse output terminal 0 and the inverse output terminal /0.

In the FET differential amplifying circuit having such a structure as explained, the FETs T₁ and T₂ form a differential amplifying circuit, and the FETs T₃ and T₄ respectively form source follower circuits. Further, the resistors R₁ and R₂ are drain load resistors of the FETs T₁ and T₂ for a direct current, respectively. Simultaneously, the load resistors become the source resistors of FETs T₃ and T₄.

Further, the drain terminals of the FETs T₁ and T₂ are directly connected to the gate terminals of the FETs T₃ and T₄, respectively. It is because a voltage is supplied to the gate terminal in the case of using a FET, so that the current would not flow. Accordingly, each drain terminal of the FETs T₁ and T₂ becomes of the same potential as the gate terminals of the FETs T₃ and T₄. Therefore, this embodiment is different from the embodiment of the amplifying circuit employing transistors, so that it becomes useless to use any condenser for impeding a direct current.

The signals outputted from the drain terminals of the FETs T₁ and T₂, such as a high-frequency signal, are supplied to the gate terminals of the FETs T₃ and T₄ and outputted from the source terminals of the FETs T₃ and T₄.

Meanwhile, as described in connection with FIGS. 23 and 24, in the conventional circuit, the voltages V_(d1) and V_(d2) were required for the differential amplifying circuit composed of the FETs T₁ and T₂ and the source follower circuits composed of the FETs T₃ and T₄, respectively. Therefore, the consumption current becomes the sum of the currents I₁₁ and I₁₂ flowing to the differential amplifying circuit and the currents I₁₃ and I₁₄ flowing to the source follower circuits.

As compared with the conventional circuit, as described above, the circuit of the present invention is formed by laying the right-side and the left-side circuits in the differential amplifying circuit lengthwise in a line, respectively. Accordingly, only one voltage V_(d1) can be used as compared with the circuit shown in FIGS. 23 and 24. Therefore, the current can be reduced to nearly half as used as the currents I₁ and I₂ flowing through the circuit.

FIG. 13 shows a schematic diagram showing a first structural example of the first embodiment of a FET differential amplifying circuit shown in FIG. 12.

That is, in the circuit shown in FIG. 13, the constant current source I₀ is formed by a series circuit composed of resistors R₅ and R₆ and the FET T₅ as compared with the FET differential amplifying circuit shown in FIG. 12. The drain terminal of the FET T₅ is connected to the source terminals of the FETs T₁ and T₂, via resistor R₅. Further, the source terminal of the FET T₅ is grounded via the resistor R₆. Simultaneously, the gate terminal is grounded directly.

Further, the circuit forms the self-bias system by grounding the gate terminals via the resistors R₃ and R₄, respectively, instead of the gate bias voltage V_(g) for supplying to the gate terminals of the FETs T₁ and T₂.

In the circuit having the above-described structure, the voltage V_(g) becomes useless, and it becomes possible to operate the circuit with only one voltage V_(d1). Further, this circuit forms two complementary inputs and two complementary outputs.

FIG. 14 shows a schematic diagram showing a second specific structure of the first embodiment of the FET differential amplifying circuit shown in FIG. 12.

Same as the structural example shown in FIG. 13, the circuit of FIG. 14 forms two complementary inputs and two complementary outputs. The circuit forms the self-bias system by grounding the gate terminals via the resistors R₃ and R₄, respectively, instead of supplying the gate bias voltage V_(g) to the gate terminals of the FETs T₁ and T₂.

In the circuit of FIG. 14, the constant current source I₀ is replaced with only resistor R₇. If stability is not required exactly, it is possible to use only such one resistor, instead of the constant current source I₀.

FIG. 15 shows a second embodiment of the FET differential amplifying circuit according to the present invention. This circuit forms one single input and one single output. A resistor R₇ has replaced the current source I₀ of the FET differential amplifying circuit shown in the embodiment of FIG. 12, similarly to the circuit shown in FIG. 14.

Further, the FET T₁ is grounded via the resistor R₃ instead of supplying the gate bias voltage V_(g) to the gate terminals of the FETs T₁ and T₂. Meanwhile, the inverse input is not used in the FET T₂, so that the FET T₂ forms the self-bias system by grounding the gate directly.

In this circuit, the inverse output of the right side of the circuit is not used. Therefore, the resistor R₈ is used instead of the FET T₄ and the resistor R₂ shown in FIG. 12.

FIG. 16 shows a third embodiment of the FET differential amplifying circuit according to the present invention. This circuit has two complementary inputs and the single output. The resistor R₇ has replaced the current source I₀ of the FET differential amplifying circuit shown in the embodiment of FIG. 12, same as in the circuit of FIG. 14.

Further, the FET T₁ is grounded via the resistor R₃ instead of supplying the gate bias voltage V_(g) to the gate terminals of FETs T₁ and T₂. Meanwhile, the FET T₂ to which the inverse input is applied forms a self-bias system, in which the FET T₂ is grounded via the resistor R₄.

In this circuit, the inverse output of the right side of the circuit is not used. The resistor R₈ has replaced the FET T₄ and the resistor R₂.

FIG. 17 shows a fourth embodiment of the FET differential amplifying circuit according to the present invention. This circuit forms the single input and two complementary outputs. The resistor R₇ has replaced the current source I₀ of the FET differential amplifying circuit shown in the embodiment of FIG. 12, same as in the circuit shown in FIG. 14.

Further, the FET T₁ is grounded via the resistor R₃ instead of supplying the gate bias voltage V_(g) to the gate terminals of the FETs T₁ and T₂. Meanwhile, the inverse input is not used in the FET T₂, so that the circuit forms the self-bias system by connecting the gate of the FET T₂ directly to the ground.

FIG. 18 shows a fifth embodiment of the FET differential amplifying circuit according to the present invention. The circuit forms two inputs and the single output. In this embodiment, the load resistors R₁ and R₂ of the differential pair of FETs T₁ and T₂ are connected in common, and the FET T₃ is inserted between the connecting point of the resistors R₁ and R₂ and the voltage source V_(d1).

Further, the gate terminal of the FET T₃ is directly connected to the drain terminal of the FET T₁, that is, one of the differential pair of the FETs T₁ and T₂.

Accordingly, the FET T₃ works as a source follower circuit. The gate terminals of the FETs T₁ and T₂ become the non-inverse input terminal I and the inverse input terminal /I, respectively. The self-bias is applied to the gate terminals by the resistors R₃ and R₄.

In the embodiment shown in FIG. 18, only the FET T₃ is provided between the differential pair of the FETs T₁ and T₂ and the voltage source to further simplify the structure of the circuit.

According to the FET differential amplifying circuits having the structures shown in FIGS. 12 through 18 as described above, the current I₁ and the current I₂ flowing to the circuit become approximately half the current I₁₁ +I₁₃ and the current I₁₂ +I₁₄, in comparison with the conventional FET differential amplifying circuits shown in FIGS. 23 and 24.

Also, it is known that a GaAs (gallium arsenide) FET is used more often as a FET in the high-frequency circuit. In the case where the amplifying circuit according to the present invention is integrated, the circuit can be a MMIC (Monolithic microwave integrated circuit) comprising FETs and resistors unitedly on a gallium arsenide wafer.

Further, it becomes possible to make the noise lower and make the consumption current lower in the differential amplifying circuit by using a HEMT (High Electron Moving Transistor), in which noise is lower than that of the GaAs FET used as a FET.

According to the present invention the amplifying circuit of which noise is lower and consumption current is lower can be obtained. Further, amplifying elements such as transistors, FETs or HEMTs can be used according to the principle of the present invention.

Therefore, it is possible to apply the present invention to each kind of amplifying circuits, that are indispensable in compact type handy machines, and particularly, portable telephones. Thus, it is apparent that the present invention greatly contributes to industrial efficiency.

Although the present invention has been described with reference to embodiments, the present invention is not restricted to those. It should be, of course, understood that those embodiments which are the same as the technical concept of the invention are within the protective scope of this invention. 

What is claimed is:
 1. A transistor amplifying circuit comprising:a first transistor having a base of an input terminal, to which a first base bias is supplied, a second transistor having a collector connected to a voltage source, a base supplied with a second base bias and an emitter of an output terminal, a parallel circuit of a constant current source connected to an emitter of the first transistor and a first condenser, an inductor connected between a collector of the first transistor and an emitter of the second transistor; and a second condenser connected between the collector of the first transistor and the base of the second transistor.
 2. A transistor amplifying circuit according to claim 1, further comprising a resistor, which connects the base of the second transistor to the voltage source.
 3. A transistor amplifying circuit according to claim 1, wherein the constant current source is a resistor, which is connected to the second condenser in parallel.
 4. A transistor amplifying circuit according to claim 1, wherein the constant current source is a series circuit of a third transistor and the resistor connected to an emitter of the third transistor, and the series circuit is connected to the second condenser in parallel.
 5. A transistor amplifying circuit according to claim 1, further comprising a third condenser connected to the inductor in parallel to form a resonant tank circuit.
 6. A transistor amplifying circuit according to claim 1, further comprising a bias circuit section that includes a voltage level shift circuit having a plurality of diodes connected in series, of which one end is connected to the voltage source, for providing predetermined potentials, which are supplied to the bases of the first through third transistors.
 7. A transistor amplifying circuit according to claim 6, further comprising a forth transistor, which is inserted in the voltage level shift circuit and a base of which is supplied with a predetermined voltage.
 8. A transistor amplifying circuit according to claim 1, wherein the base of the first transistor is supplied with a high frequency signal and a high frequency output signal is outputted from the emitter of the second transistor.
 9. A semiconductor device having a semiconductor integrated circuit, comprising;a first transistor having a base of an input terminal, to which a first base bias is supplied, a second transistor having a collector connected to a voltage source, a base supplied with a second base bias and an emitter of an output terminal, a parallel circuit of a constant current source connected to an emitter of the first transistor and a first condenser, an inductor connected between a collector of the first transistor and an emitter of the second transistor; and a second condenser connected between the collector of the first transistor and the base of the second transistor, wherein the size of the emitter of the first transistor is larger than that of the second transistor.
 10. A transistor differential amplifier circuit comprising:a differential pair including first and second transistors, first and second resistors connected to collectors of the first and second transistors and a constant current source connected commonly to emitters of the first and second transistors; a third transistor, an emitter of which is connected to a connection point of the first and second resistors and outputs an output signal; a first condenser connected between the collector of the first transistor and a base of the third transistor; and a voltage source connected directly to a collector of the third transistor.
 11. A transistor differential amplifying circuit according to claim 10, further comprising;third and fourth resistors, a constant voltage source for providing base biases to the bases of the first and second transistors via the third and fourth resistors, respectively, a fifth resistor connected between the base of the third transistor and the voltage source for providing a base bias to the base of the third transistor from the voltage source.
 12. A transistor differential amplifier circuit comprising;a differential pair including first and second transistors, first and second inductors connected to collectors of the first and second transistors and a constant current source connected commonly to emitters of the first and second transistors, a third transistor, an emitter of which is connected to a connection point of the first and second inductors, a first condenser connected between the collector of the first transistor and a base of the third transistor; and a voltage source connected to the collector of the third transistor, an output being outputted from the emitter of the third transistor.
 13. A transistor amplifying circuit comprising:a differential pair including first and second transistors, a base of the first transistor being supplied with an input signal and a base of the second transistor being supplied with a control signal, first and second resistors connected to collectors of the first and second transistors, and a constant current source connected commonly to emitters of the first and second transistors; a third transistor, an emitter of which is connected to a connection point of the first and second resistors and outputs an output signal; a first condenser connected between the collector of the first transistor and a base of the third transistor; a second condenser connected between the base of the second transistor and the ground; a voltage source connected directly to the collector of the third transistor; third and fourth resistors; a constant voltage source for providing base biases to the bases of the first and second transistors via the third and fourth resistors, respectively; and a fifth resistor connected between the base of the third transistor and the voltage source for providing a base bias to the base of the third transistor from the voltage source.
 14. A transistor amplifying circuit comprising:a differential pair including first and second transistors, first and second resistors connected to collectors of the first and second transistors, and a constant current source connected commonly to emitters of the first and second transistors; a third transistor, an emitter of which is connected to a connection point of the first and second resistors and outputs an output signal; a first condenser connected between the collector of the first transistor and a base of the third transistor; and a voltage source connected directly to the collector of the third transistor, wherein the sizes of the first and second transistors are same and the size of the third transistor is smaller than that of the first and second transistors. 